Interfaces

Systems

Various

Puxing PX-888

The Puxing PX-888 is a cheap Chinese portable transceiver. Different versions exist: VHF-, UHF- and dual band.
The microphone socket can be modified to carry the unfiltered demodulated signal

The receiver IC is a TA31136, with the unfiltered audio on pin 9.

PX-888

To open the transceiver, the two knobs need to be removed. After that, the three washers can be loosened using a pair of fine tip pliers.

Next, the back part of the transceiver can be taken apart from the front half, starting at the bottom. To make the two halves easier to handle, also the flatcable connecting the two halves
can be loosened.

Schematic microphone socket

Microphone socket

Connection of the discriminator tap

Schematic receiver IC

The microphone socket is reused, so no drilling is required.

Follow the next steps to add a discriminator tap:

Remove the SMD resistor in the blue circle. This isolates the tip of the chassis socket (see schematic diagram)

Solder a 10 k, 1/8 W resistor to the contact marked with the orange arrow

Connect the resistor's other lead to a piece of insulated wire

Solder the other end of the wire to point 'DEV'. This point connects directly to pin 9 of the TA31136 receiver IC

Using a 3.5 mm (1/8") mono or stereo plug, the unfiltered audio is available on the tip and ground.

This modification does not affect the operation of the radio. Both an external speaker/microphone and the USB programming cable still work correctly.